7.1 Configure the Gateway Initialization Parameter File

7.1.1 Choose a System Identifier for the Gateway

The gateway system identifier (SID) is an alphanumeric character string that identifies a gateway instance. You need one gateway instance, and therefore one gateway SID, for each Teradata database you are accessing. The SID is used as part of the file name for the initialization parameter file. The default SID is dg4tera.

You can define a gateway SID, but using the default of dg4tera is easier because you do not need to change the initialization parameter file name. However, if you want to access two Teradata databases, you need two gateway SIDs, one for each instance of the gateway. If you have only one Teradata database and want to access it sometimes with one set of gateway parameter settings, and other times with different gateway parameter settings, then you will need multiple gateway SIDs for the single Teradata database.

7.1.2 Customize the Initialization Parameter File

The initialization parameter file must be available when the gateway is started. During installation, the following default initialization parameter file is created:

$ORACLE_HOME/dg4tera/admin/initdg4tera.ora

Where $ORACLE_HOME is the directory under which the gateway is installed.

This initialization file is for the default gateway SID. If you are not using dg4tera as the gateway SID, you must rename the initialization parameter file using the SID you chose in the preceding step "Choose a System Identifier for the Gateway". This default initialization parameter file is sufficient for starting the gateway, verifying a successful installation, and running the demonstration scripts.

A number of initialization parameters can be used to modify the gateway behavior. Refer to Appendix C, "Initialization Parameters"for the complete list of initialization parameters that can be set. Changes made to the initialization parameters only take effect in the next gateway session. The most important parameter is the HS_FDS_CONNECT_INFO, which describes the connection to the non-Oracle system.

The default initialization parameter file already has an entry for this parameter. The syntax for HS_FDS_CONNECT_INFO is as follows:

HS_FDS_CONNECT_INFO=host_alias:port_number[/database_name]

Where:

Variable

Description

host_alias

is the host alias name or IP address of the machine hosting the Teradata database.

port_number

is the port number of the Teradata database server.

database_name

is the Teradata database name.

This release of gateway can support IPv6. If IPv6 address format is to be specified, you have to wrap it with square brackets to indicate the separation from the port number. For example,

7.2.1 Configure Oracle Net Listener for the Gateway

The Oracle Net Listener listens for incoming requests from the Oracle database. For the Oracle Net Listener to listen for the gateway, information about the gateway must be added to the Oracle Net Listener configuration file, listener.ora. This file by default is located in $ORACLE_HOME/network/admin, where $ORACLE_HOME is the directory under which the gateway is installed.

The following entries must be added to the listener.ora file:

A list of Oracle Net addresses on which the Oracle Net Listener listens.

The executable name of the gateway that the Oracle Net Listener starts in response to incoming connection requests.

A sample of the listener.ora entry (listener.ora.sample) is available in the $ORACLE_HOME/dg4tera/admin directory where $ORACLE_HOME is the directory under which the gateway is installed.

7.2.1.1 Syntax of listener.ora File Entries

The Oracle database communicates with the gateway using Oracle Net and any supported protocol adapters. The following is the syntax of the address on which the Oracle Net Listener listens using the TCP/IP protocol adapter:

specifies the port number used by the Oracle Net Listener. If you have other listeners running on the same machine, then the value of port_number must be different from the other listeners' port numbers.

To direct the Oracle Net Listener to start the gateway in response to incoming connection requests, add an entry to the listener.ora file.

Note:

You must use the same SID value in the listener.ora file and the tnsnames.ora file that will be configured in the next step.

specifies the SID of the gateway. Matches the gateway SID specified in the connect descriptor entry in the tnsnames.ora file.

oracle_home_directory

specifies the Oracle home directory where the gateway resides.

teradata_client_library_directory

specifies the directory where the Teradata client directory resides.

dg4tera

specifies the executable name of the Oracle Database Gateway for Teradata.

If you already have an existing Oracle Net Listener, then add the following syntax to SID_LIST in the existing listener.ora file. Note the syntax provided below is for Linux 32 bit. Refer to the above section for other platforms.

In this example, the service name is dg4tera, which is the default SID value assigned during installation.

7.3 Configure the Oracle Database for Gateway Access

Before you use the gateway to access Teradata data you must configure the Oracle database to enable communication with the gateway over Oracle Net.

To configure the Oracle database you must add connect descriptors to the tnsnames.ora file. By default, this file is in $ORACLE_HOME/network/admin, where $ORACLE_HOME is the directory in which the Oracle database is installed. You cannot use the Oracle Net Assistant or the Oracle Net Easy Config tools to configure the tnsnames.ora file. You must edit the file manually.

A sample of the tnsnames.ora entry (tnsnames.ora.sample) is available in the $ORACLE_HOME/dg4tera/admin directory where $ORACLE_HOME is the directory under which the gateway is installed.

7.3.1 Configuring tnsnames.ora

Edit the tnsnames.ora file to add a connect descriptor for the gateway. The following is the syntax of the Oracle Net entry using the TCP/IP protocol:

is the description of the object to connect to as specified when creating the database link, such as dg4tera.

Check the sqlnet.ora file for the following parameter setting:

names.directory_path = (TNSNAMES)

Note: The sqlnet.ora file is typically stored in $ORACLE_HOME/network/admin.

TCP

is the TCP protocol used for TCP/IP connections.

host_name

specifies the machine where the gateway is running.

port_number

matches the port number used by the Oracle Net Listener that is listening for the gateway. The Oracle Net Listener's port number can be found in the listener.ora file used by the Oracle Net Listener. See "Syntax of listener.ora File Entries".

7.4 Create Database Links

Any Oracle client connected to the Oracle database can access Teradata data through the gateway. The Oracle client and the Oracle database can reside on different machines. The gateway accepts connections only from the Oracle database.

A connection to the gateway is established through a database link when it is first used in an Oracle session. In this context, a connection refers to the connection between the Oracle database and the gateway. The connection remains established until the Oracle session ends. Another session or user can access the same database link and get a distinct connection to the gateway and Teradata database.

Database links are active for the duration of a gateway session. If you want to close a database link during a session, you can do so with the ALTER SESSION statement.

To access the Teradata server, you must create a database link. A public database link is the most common of database links.

7.5 Configure Two-Phase Commit

The gateway supports the following transaction capabilities:

COMMIT_CONFIRM

READ_ONLY

SINGLE_SITE

The transaction model is set using the HS_TRANSACTION_MODEL initialization parameter. By default, the gateway runs in COMMIT_CONFIRM transaction mode. When the Teradata database is updated by a transaction, the gateway becomes the commit point site. The Oracle database commits the unit of work in the Teradata database after verifying that all Oracle databases in the transaction have successfully prepared the transaction. Only one gateway instance can participate in an Oracle two-phase commit transaction as the commit point site.

The log table, called HS_TRANSACTION_LOG, is where two-phase commit transactions are recorded. Alternatively users can specify a different table name by setting a gateway initialization parameter HS_FDS_TRANSACTION_LOG parameter. This table needs to be in the same schema as the recovery account.

7.5.1 Create a Recovery Account and Password

For the gateway to recover distributed transactions, a recovery account and password must be set up in the Teradata database. By default, both the user name of the account and the password are RECOVER. The name of the account can be changed with the gateway initialization parameter HS_FDS_RECOVERY_ACCOUNT. The account password can be changed with the gateway initialization parameter HS_FDS_RECOVERY_PWD.

Note:

Oracle recommends that you do not use the default value RECOVER for the user name and password. Moreover, storing plain-text as user name and password in the initialization file is not a good security policy. There is now a utility called dg4pwd that should be used for encryption. Refer to Section 4.2.3, 'Encrypting Initialization parameters' in the Oracle Database Heterogeneous Connectivity User's Guide for further details.

Set up a user account in the Teradata database. Both the user name and password must be a valid Teradata user name and password.

In the initialization parameter file, set the following gateway initialization parameters:

HS_FDS_RECOVERY_ACCOUNT to the user name of the Teradata user account you set up for recovery.

HS_FDS_RECOVERY_PWD to the password of the Teradata user account you set up for recovery.

7.5.2 Create the Transaction Log Table

When configuring the gateway for two-phase commit, a table must be created in the Teradata database for logging transactions. The gateway uses the transaction log table to check the status of failed transactions that were started at the Teradata database by the gateway and registered in the table.

Note:

Updates to the transaction log table cannot be part of an Oracle distributed transaction.

Note:

The information in the transaction log table is required by the recovery process and must not be altered. The table must be used, accessed, or updated only by the gateway.

Create the transaction log table in the user account you created in "Create a Recovery Account and Password". Because the transaction log table is used to record the status of a gateway transaction, the table must reside at the database where the Teradata update takes place. Also, the transaction log table must be created under the owner of the recovery account.

Note:

To utilize the transaction log table, users of the gateway must be granted privileges on the table.

To create a transaction log table use the dg4tera_tx.sql script, located in the directory $ORACLE_HOME/dg4tera/admin, where $ORACLE_HOME is the directory under which the gateway is installed.

7.6Encrypt Gateway Initialization Parameter Values

The gateway uses user IDs and passwords to access the information in the remote database. Some user IDs and passwords must be defined in the gateway initialization file to handle functions such as resource recovery. In the current security conscious environment, having plain-text passwords that are accessible in the initialization file is deemed insecure. The dg4pwd encryption utility has been added as part of Heterogeneous Services to help make this more secure. This utility is accessible by this gateway. The initialization parameters that contain sensitive values can be stored in an encrypted form.

See Also:

Oracle Database Heterogeneous Connectivity Administrator's Guide for more information about using this utility.

7.7 Configure the Gateway to Access Multiple Teradata Databases

The tasks for configuring the gateway to access multiple Teradata databases are similar to the tasks for configuring the gateway for a single database. The configuration example assumes the following:

The gateway is installed and configured with the default SID of dg4tera

The ORACLE_HOME environment variable is set to the directory where the gateway is installed.

The gateway is configured for one Teradata database named db1.

Two Teradata databases named db2 and db3 on a host with IP Address 204.179.79.15 are being added.

7.7.1 Multiple Teradata Databases Example: Configuring the Gateway

Choose One System ID for Each Teradata Database

A separate instance of the gateway is needed for each Teradata database. Each instance needs its own gateway System ID (SID). For this example, the gateway SIDs are chosen for the instances that access the Teradata databases:

dg4tera2 for the gateway accessing database db2.

dg4tera3 for the gateway accessing database db3.

Create Two Initialization Parameter Files

Create an initialization parameter file for each instance of the gateway by copying the original initialization parameter file: $ORACLE_HOME/dg4tera/admin/initdg4tera.ora, twice, naming one with the gateway SID for db2 and the other with the gateway SID for db3:

Change the value of the HS_FDS_CONNECT_INFO parameter in the new files.

For initdg4tera2.ora, enter the following:

HS_FDS_CONNECT_INFO=204.179.79.15:1025/db2

For initdg4tera3.ora, enter the following:

HS_FDS_CONNECT_INFO=204.179.79.15:1025/db3

Note:

If you have multiple gateway SIDs for the same Teradata database because you want to use different gateway parameter settings at different times, follow the same procedure. You create several initialization parameter files, each with different SIDs and different parameter settings.

The value for PORT is the TCP/IP port number of the Oracle Net Listener that is listening for the gateway. The number can be found in the listener.ora file used by the Oracle Net Listener. The value for HOST is the name of the machine on which the gateway is running. The name also can be found in the listener.ora file used by the Oracle Net Listener.

7.7.5 Multiple Teradata Databases Example: Accessing Teradata Data

Enter the following to create a database link for the dg4tera2 gateway: